Integral end course for multilayer pressure vessels



Filed Dec. 22, 1961 INTEGRAL END couRsE FOR MULTILAYER PRESSURE vEssELs la n /2 /5 April 7, 1964 Inl!"` f INVENTOR. E WALD E ScHM/Tz Howard j Barne /ITfoRNEY "//l/l//l/ 2 United States Patent O INTEGRAL END COURSE FR MULTILAYER PRESSURE VESSELS Ewald F. Schmitz, Milwaukee, Wis., assigner, by mesne assignments, to Chicago Bridge & Iron Company, Oak Brook, Ill., a corporation of Illinois Filed Dec. 22, 1961, Ser. No. 161,649 3 Claims. (Cl. 220-3) This invention relates to an integral end course for a Multilayer pressure vessel, and more particularly, to an integral Multilayer end course providing means for attaching an end closure directly to the Multilayer vessel without the requirement of a shrink ring.

In the past, the practice has been to fabricate separate forged end courses for Multilayer vessels and then weld these to the vessel shell to provide an attachment means for the end closure of the vessel. Direct attachment of the end closure to the vessel shell by means of stud bolts has been tried, but, prior to this invention, severe axial loads transmitted to the vessel by the stud bolts having standard 60 threads would tend to spread the layers of the vessel apart at the points where the end closure stud bolts were threaded into the vessel. Spreading of the layers cannot be tolerated, of course, because it seriously deforms and weakens the vessel at the end closure joint. which is already a critical stress region.

This invention avoids the necessity of fabricating a separate forging, and thereby eliminates the girth weld which was required to secure the end forging to the Multilayer vessel shell. More specifically, this invention provides a strong, integral end course construction having a deposit welded end surface.

The deposit welded end surface simply and conveniently overcomes the problem of spreading of the layers of the vessel in the vicinity of the end closure stud bolts and provides an economical attachment means for the end closure of a Multilayer vessel. In addition, it has been found that the end closure attachment is made even stronger by employing a stud bolt of a thread form having a pressure fiank angle less than the standard 60 thread, such as a modified square thread, or a buttress thread.

This invention combines the simple stud bolted end closure means used in solid Wall forged pressure vessels with the strength advantages of the Multilayer construction exemplified by U.S. Patent Re. 22,251, reissued J anuary 12, 1943 to Stresau and assigned to a common assignee.

The best mode presently contemplated for carrying out the invention is illustrated in the accompanying drawings in which:

FIGURE 1 is a longitudinal section of the Multilayer vessel constructed in accordance with the invention;

FIG. 2 is an enlarged fragmentary sectional view of the vessel showing the attachment of the end closure to the end course of the shell;

FIG. 3 is an enlarged sectional view taken on line 3-3 of FIG. 2; and

FIG. 4 is an end view taken on line 4-4 of FIGURE l with a portion of the end surface weld broken away.

As shown in the drawings, a vessel 1 of Multilayer construction includes a closed end section 2, a cylindrical body section 3, and an open end 4, enclosed by an end closure 5. The closed end section 2 is attached to the body section 3 by means of a girth weld 6. The closed end section 2 is shown as a solid forging, but it may also be of Multilayer construction, similar to the body Section 3, which comprises a plurality of sheet metal layers 7 disposed tightly around an inner, fluidtight layer 8.

The body section 3 is provided with vents 9 in the layers 7 so that excessive pressure will not build up if the inner fluid-tight layer 9 develops a leak. The number of 3,l23,00l Patented Apr. 7, 1964 "ice layers 7 is determined by the operating requirements for the vessel 1.

The open end of vessel 1 is provided with a plurality of threaded openings 10 which are tapped into the end of the layers 7. The threaded openings 10 are adapted to receive stud bolts 11 which extend outwardly from the end section 4 through bolt openings 12 in the end closure 5.

Each stud bolt 11 has a nut 13, and two threaded ends 14 and 1S. As best shown in FIG. 2, the threaded stud end 15 of each stud bolt 11 is provided with a thread form having a pressure flank angle of less than a standard 60 thread. As shown in FIG. 2, the pressure flank angle is preferably 7 or less. The almost square or buttress shaped thread is very important to the success of the end closure attachment means of the invention because the greatest possible amount of the axial load on the end closure is transferred to the body section 3, and is uniformly distributed as an axial load between the respective layers 7. The threaded shank of each stud bolt firmly engages and is retained by each layer 7, and the head 13 is tightened down on the end closure 5 so that the end closure 5 is tightly sealed to the vessel 1.

Under very severe loading conditions, the layers 7 may tend to spread in the vicinity of the stud bolts 11. When severe loading is expected, Weld metal 16 is deposited on the end of the cylindrical shell body section 3 prior to tapping the bolt holes 10 to effectively prevent the spreading of the layers 7.

In actual tests of the end course closure attachment of this invention, the layers 7 held their shape with no distortion, and failure occurred in the shank of the stud bolt 11. The failure at the stud bolts was remedied by increasing their number, thereby decreasing the axial load on each one.

A unique advantage obtained by the end closure attachment means of this invention is that the axial load on the end closure 5 is perfectly distributed to all layers 7 of the vessel throughout the length of the vessel. This would not be true, for example, in a spirally wrapped vessel of the type disclosed by Schierenbeck, U.S. Patent 2,326,176, in which adjacent strips are held together by overlapping notches in the strip, or in the spirally wrapped vessel shown in the Fergusson, Patent 2,600,630, which has spiral Welds throughout its length to secure adjacent strips together.

In applicants invention, each layer 7 shares a portion of the axial load throughout its length. As the radial load on the vessel increases, the inner layers 7 are more tightly disposed against the outer layers 7, thereby tightening the engagement of the stud bolts 11 with the layers 7 of the vessel shell, so that the end closure 5 is more firmly held on the vessel..

The need for a shrink ring is completely eliminated by the integral end course construction of this invention. Because the end of the layers at the open end 4 of the body section 3 are deposit Welded, they act as a single, integral end course and thereby eliminate the end forging and girth seam Weld which was formerly required for attaching the forging to the vessel body section.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. In a Multilayer pressure vessel, a cylindrical Wall section composed of a series of superimposed concentric cylindrical layers, said wall section having an annular end surface defined by the ends of said concentric layers, and a Weld deposit disposed on said annular end surface and connecting the ends of the individual layers together, said end surface and said weld deposit having a plurality of E generally square threaded bolt-receiving passages therein disposed axially parallel to the longitudinal axis of said vessel.

2. In a Multilayer pressure vessel, a cylindrical wall section composed of a series of superimposed concentric cylindrical layers, said Wall section having an annular end surface defined by the ends of said concentric layers, a weld deposit disposed continuously over the annular end surface and connecting the ends of the individual layers together, said end surface and said weld deposit having a plurality of bolt-receiving passages therein disposed axially parallel to the longitudinal axis of said vessel, said bolt-receiving passages being internally threaded and having a pressure iiank angle less than 7, an end closure disposed directly against said Weld deposit and having a series of openings located in alignment with said passages, and a plurality of bolts disposed Within said openings and threaded into said passages, said bolts being externally threaded and having a pressure ank angle to complement that of said passages.

3. The apparatus of claim 1 in which the passages are substantially square threaded having a thread surface angle ranging from 90 to 97 from the longitudinal axis of said passages.

References Cited in the le of this patent UNITED STATES PATENTS 2,326,176 Schierenbeck Aug. 10, 1943 2,337,247 Y Kepler Dec. 21, 1943 2,772,102 Webb Nov. 27, 1956 

2. IN A "MULTILAYER" PRESSURE VESSEL, A CYLINDRICAL WALL SECTION COMPOSED OF A SERIES OF SUPERIMPOSED CONCENTRIC CYLINDRICAL LAYERS, SAID WALL SECTION HAVING AN ANNULAR END SURFACE DEFINED BY THE ENDS OF SAID CONCENTRIC LAYERS, A WELD DEPOSIT DISPOSED CONTINUOUSLY OVER THE ANNULAR END SURFACE AND CONNECTING THE ENDS OF THE INDIVIDUAL LAYERS TOGETHER, SAID END SURFACE AND SAID WELD DEPOSIT HAVING A PLURALITY OF BOLT-RECEIVING PASSAGES THEREIN DISPOSED AXIALLY PARALLEL TO THE LONGITUDINAL AXIS OF SAID VESSEL, SAID BOLT-RECEIVING PASSAGES BEING INTERNALLY THREADED AND HAVING A PRESSURE FLANK ANGLE LESS THAN 7 DEGREES, AN END CLOSURE DISPOSED DIRECTLY AGAINST SAID WELD DEPOSIT AND HAVING A SERIES OF OPENINGS LOCATED IN ALIGNMENT WITH SAID PASSAGES, AND A PLURALITY OF BOLTS DISPOSED WITHIN SAID OPENINGS AND THREADED INTO SAID PASSAGES, SAID BOLTS BEING EXTERNALLY THREADED AND HAVING A PRESSURE FLANK ANGLE TO COMPLEMENT THAT OF SAID PASSAGES. 